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Sunday, September 23, 2012

Scientists Aim to Put a Pox On Dog Cancer

World Hot Topics Blog

Scientists Aim to Put a Pox On Dog Cancer

ScienceDaily Researchers report that
myxoma -- a pox virus that afflicts rabbits but not humans, dogs or any other
vertebrates so far studied -- infects several different types of canine cancer
cells in cell culture while sparing healthy cells. The study adds to the
evidence that viruses or modified viruses will emerge as relatively benign
cancer treatments to complement or replace standard cancer therapies.

The new study, reported in the American
Journal of Veterinary Research, is unique in that it focused on
spontaneously occurring cancers in dogs. This allowed the researchers to avoid
a common practice: testing viral therapies on mice or rats with induced human
cancers. Such animals must be immunosuppressed to prevent their immune systems
from rejecting the foreign tissue, complicating the results.

Treating cancers with viruses could
offer several advantages over standard cancer therapies, said University of
Illinois veterinarian and pathobiology professor Amy MacNeill, who led the new
study. Many cancers have impaired anti-viral defenses, which allow viruses to
target tumors while sparing healthy cells. And under the right conditions,
infection with an oncolytic (cancer-killing) virus exterminates cancer cells
and elicits an anti-cancer immune response without spurring a harmful
inflammatory response, she said. Chemotherapy and radiation kill healthy cells
along with cancer cells and radiation can cause abrupt cell death that spurs
inflammation and pain, she said. World Hot Topics Blog.

"Ideally, what would happen is
the virus would get into a few cancer cells, cause cell death and then spread
to the other tumor cells nearby," she said.

Recent studies have shown that
oncolytic viral therapies can be used successfully in conjunction with
traditional approaches, MacNeill said.

"There was a study in cats
where they removed the tumor surgically and then they put a viral therapy in
the area where the tumor had been removed," she said. The animals that
received the viral therapy had significantly less regrowth of the cancer than
those that weren't exposed to the virus after surgery.

"Other studies (1, 2, 3, 4)
have shown that once you've eliminated a cancer with an oncolytic virus, if you
re-challenge that animal with the same cancer cells, they don't develop
tumors," MacNeill said. Viral infection of the cancer cells appears to
train the immune system to better recognize the cancer, she said.

In the new study, the researchers
wanted to see if spontaneously occurring cancers in dogs were responsive to
infection with a virus that is not a pathogen in humans or dogs. They found
that cancerous and healthy canine cells respond as human cells do to myxoma
infection: The virus invades cancer cells and leaves healthy cells alone. The
team also showed that a version of the myxoma virus with a single gene deleted
was four times better at killing cancer cells than the unmodified virus. The
deleted gene codes for a protein that hinders cell death in infected cells.

More preliminary tests are needed
and researchers have many more years of tests and trials ahead, but if all goes
well they will eventually test the virus or a modified version of the virus in
dogs with cancer, MacNeill said.

"We wanted to make sure that
the dog cells were like the human cells because we want to use these viruses
not only to cure dogs of cancer but also to use the dogs as better models for
humans with cancer," she said. "People are beginning to see the logic
of this approach. These dogs have spontaneous tumors just like humans, they're
living in the same environment as humans, they're exposed to the same
carcinogens in the water if there are any and they sometimes even share our
food."

She calls this approach a
"win-win" for dogs and humans.

"This way we can test the
therapy in dogs while at the same time treating them," she said.
"Other researchers can take our results and use them to develop therapies
for human patients."

The study team also included
researchers from the University of Florida.